No, I think it is enough to have the content directory name as a configurable option.
I see one required change to what I posted earlier in my proposed structure that should be made. We should not use 'xhtml' as a subdirectory name within the content directory, but rather it should just be 'text'.
mimetype
META-INF/
com.apple.ibooks.display-options.xml
container.xml
EPUB/ <<configurable>>
fonts/
font.otf
images/
cover.jpg
fig1.jpg
styles/
stylesheet.css
content.opf
toc.ncx
text/
ch001.xhtml